Control of headbox stock characteristics

ABSTRACT

THIS INVENTION IS DIRECTED TO APPARATUS FOR CONTROLLING THE CHARACTERISTICS OF STOCK DELIVERED TO A HEADBOX OF A PAPERMAKING MACHINE. THE STOCK OF DIFFERENT CONSISTENCIES ARE CONTAINED IN A PLURALITY OF STCK RESERVOIRS AND THE STOCK FROM EACH OF THE RESERVOIRS IS DELIVERED TO A MAIN STOCK CHAMBER WHERE THE STOCK IS MIXED TOGETHER TO FORM A STOCK OF A DESIRED CONSISTENCY. THE STOCK FROM THE MAIN STOCK CHAMBER IS THEN DELIVERED VIA A FLOW CONTROL VALVE TO A STOCK SCREENING APPARATUS WHERE THE STOCK IS FINALLY SCREENED BEFORE BEING DELIVERED TO A HEADBOX OF A PAPERMAKING MACHINE. THE TEMPERATURE OF THE STOCK IS MEASURED PRIOR TO THE STOCK ENTERING THE SCREENING APPARATUS, AND THE PRESSURE DROP OF THE STOCK PASSING THROUGH THE APPARATUS IS MEASURED. THE MEASURED PRESSURE DROP AND TEMPERATURE OF THE STOCK IS THEN COMPUTED TO DEVELOP CONTROL SIGNALS TO CONTROL T HE FLOW OF STOCK TO THE SCREENING APPARATUS THEREBY MAINTAINING THE STOCK DELIVERED TO THE HEADBOX AT A DESIRED CHARACTRISTIC.   D R A W I N G

June 29, 1971 s, M SALOMON I 3,589,980

CONTROL 0F HEADBOX STOCK CHACTERISTICS .5u @Ma/v /W 53u @Ma/v June 29, 1971 s. M. SALOMON CONTROL OF HEADBOX'STOCK CHACTERISTICS Filed Jan. 2, 1968 2 Smeets-sheet 2 United States Patent Oice 3,589,980 Patented June 29, 1971 3,589,980 CONTROL OF HEADBOX STOCK CHARACTERISTICS Salomon M. Salomon, Madison, Wis., assigner to Beloit Corporation, Beloit, Wis. Filed Jan. 2, 1968, Ser. No. 694,997 Int. Cl. D21f 1/08 U.S. Cl. 162-258 2 Claims ABSTRACT OF THE DISCLOSURE This invention is directed to apparatus for controlling the characteristics of stock delivered to a headbox of a papermaking machine. The stock of different consistencies are contained in a plurality of stock reservoirs and the stock from each of the reservoirs is delivered to a main stock chamber where the stock is mixed together to form a stock of a desired consistency. The stock from the main stock chamber is then delivered via a flow control valve to a stock screening apparatus where the stock is finally screened before being delivered to a headbox of a papermaking machine. The temperature of the stock is measured prior to the stock entering the screening apparatus, and the pressure drop of the stock passing through the apparatus is measured. The measured pressure drop and temperature of the stock is then computed to develop control signals to control the ow of stock to the screening apparatus thereby maintaining the stock delivered to the headbox at a desired characteristic.

BACKGROUND OF THE INVENTION Field ofthe invention This invention relates to an apparatus for screening fibrous materials suspended in liquid such as papermaking stock and the like.

The invention has special relation to stock delivery systems incorporating screening apparatus for screening the stock before the stock is finally delivered to the headbox of the papermaking machine. In the embodiment disclosed herein the screening apparatus includes a vertically extending cylindrical screen having respective inner and outer screen members spaced radially apart to form a chamber therebetween for receiving material of desired consistency and deli-vering the material to the output of the screening apparatus. Means are provided within the screening apparatus to measure the pressure drop either between the input and output of the apparatus or to measure the pressure drop across the screening area of the apparatus.

Description of the prior art Heretofore, controlling of the characteristic of stock delivered to a headbox of a papermaking machine was accomplished by periodic manual samplings of various conditions of the stock delivered to the headbox. The information obtained by such periodic samplings was then used to determine which controls of the stock delivery system should be altered to obtain the desired stock characteristic delivered to the headbox. This manual periodic sampling would ultimately result in obtaining the desired stock characteristic issuing from the headbox onto the forming wire. However, the time delay between manual sampling and manual adjustment of the stock delivery system would cause substantial variation of the stock issuing from the headbox.

SUMMARY OF THE INVENTION Accordingly, one of the objects of the present invention is to provide a stock delivery system which automatically measures several important characteristics of the stock to develop sampling signals which are automatically computed to develop control signals to quickly and automatically vary the necessary apparatus of the control system to maintain a uniform stock characteristic issuing from the headbox.

Another object of the present invention is to provide a stock delivery system which is relatively simple in construction and easy to maintain while being highly eicient and reliable in operation.

Another object of the present invention is to provide apparatus for continuous analysis of various changes of characteristic of the stock which ows from the fan pump of the stock delivery system to the headbox, and accurately measuring the pressure drop across a screening apparatus located in uid communication prior to the headbox.

The measurement of the pressure drop of the stock passing through the screening apparatus can be accomplished in several ways. One method is to measure the upstream and downstream pressure at the inlet and outlet of the screening apparatus or in the immediate vicinity thereof and compare the pressure readings to obtain the accurate pressure drop between the inlet and outlet. Another method is to place pressure measuring devices in the upstream and downstream side inside the screening apparatus in the immediate vicinity of the screen plates therein.

The output information obtained from the pressure measuring devices is preferably calibrated to read in inches of water (H2O) or fractions thereof, thereby representing the pressure difference existing across the screening apparatus or across the screen plates therein. Once the flow to the screening plates is established for a given mechanical adjustment, the only changing condition in the system which will create varying pressure drops in the screening apparatus is the consistency or quantity and quality of the stock being supplied to the screening apparatus.

It has been found by experimentation that for a xed mechanical condition of the screening apparatus, that is a Vgiven stock flow, the consistency of the recirculating stock could be brought to the desired level with the addition of heavy stock to the system. This is accomplished by watching the changes in pressure drop across the screening apparatus.

According to the present invention these variations are used to produce continuous sampling signals which are then delivered to a computer with other important available data. The computer then develops several control signals to automatically control the operation of various components of the stock delivery system to maintain the output of the system at a desired stock characteristic.

Accordingly, other objects, features and advantages will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings in which like reference numerals throughout the various views of the drawings are intended to designate similar elements or components.

yBRIEF DESCRIPTION OF THE DRAWINGS FI'G. l is a schematic diagram illustrating a stock delivery system constructed in accordance with the principles of this invention; and

FIG. 2 is an elevational View which is partly broken away in vertical section to show the screening apparatus constructed in accordance with the principles of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Seen in FIG. 1 is a stock ow control system constructed in accordance with the principles of this invention, and is designated generally by reference numeral 100. The control system 100 includes a stock screening apparatus for delivering stock of desired consistency toa headbox 101. The pressure drop between the stock entering the screening apparatus 10 and the stock leaving the screening apparatus is measured by a pressure cell 102 which, in turn, is connected to the input and output of the apparatus 10 via lines 103 and 104 respectively. According to the present invention, the continuous sampling of the pressure drop of stock passing through the screening apparatus 10 provides important information which can be used to control the characteristics of the stock delivered to the headbox 101. Although the pressure cell 102 is shown as receiving pressure from the input and output of the screening device 10 it will be understood that independent pressure cells may be located Within the screening device to measure pressure drops at the desired locations within the device.

A stock slurry having the desired characteristics is accumulated in a main stock receiving chamber 1.0.6. A plurality of stock reservoirs 107, 108, 109 and 110 supply the main receiving chamber 106 with stock of different characteristics thereby mixing the stock and forming a stock slurry of the desired characteristic in the chamber 106. The reservoir 107 is connected to the chamber 106 via a iiow control valve 111 and a ow meter 112. Similarly, the reservoir 108 is connected to the chamber 106 via a now control Valve 113 and a flow meter 114, and reservoir 1-09 is connected to the chamber 106 via a flow control valve 115 and a ow meter 116. Similarily, reservoir 110 is connected to the chamber 106 via a flow control valve 117 and a flow meter 118.

Each of the flow control valves 111, 113, 115 and 117 are provided -with controller devices 111a, 113a, 115a and 117a respectively for controlling the quantity of stock owing through the valve. IEach of the controllers 111a, 113a, 115a and 117a is connected to a computer control system 120.

The computer control system 120 continuously evaluates Various parameters of the control system and provides control signals to the controllers within the control system to continuously maintain the stock delivered to the headbox 101 at a desired characteristic. Therefore, each of the flow meters 112, 114, 116 and 118 is provided With a readout line 121, 122, 123 and 124 respectively which are connected to the computer control system 120 to provide continuous sampling information as to the gallonagey of stock delivered to the main chamber 106 from each of the reservoirs 107-110.

The stock of a predetermined consistency is then delivered from the output of the chamber 106 to a flow control fvalve 126 which has a controller 126e thereof connected to the computer 120 rvia a line 127. The output of the control valve 126 is connected to a flow meter 128 which, in turn, is connected to the computer 120 via a line 129. Connected in fluid communication with the flow meter 128 is a fan pump 130 via a conduit 131. Also connected to the fan pump 130 is a white water reservoir 132 from the Wire pit of the paper making machine. The reservoir 132 is connected to the fan pump via a conduit 133. Steam is introduced into the reservoir 132 via Ia conduit 134 and a flow control Valve 136 which, in turn, has a controller 136e connected to the computer control system 120 via a line 137. By controlling the amount of steam introduced into the white Water 'Within the reservoir 132 the temperature of the stock may be maintained within a predetermined range of temperatures.

The output of fan pump 130 is connected to a temperature sensing device 13-8 through a conduit 139. The temperature sensing device 138 measures the temperature of the stock and produces a continuous sampling signal of the temperature at that point in the stock delivery system. The electrical output of the temperature sensing device is connected to the computer control system :via a line 138a, and the stock output of the temperature sensing device is delivered to a flow meter 148 and a ilow control valve 141. The flow control valve 141 is connected in uid communication with a conduit 140 which, in turn, is connected to the input of the fan pump 130. Therefore, the conduit 140 together with the flow control valve 141 provide a recirculating path for excess stock leaving the fan pump 130. The flow control valve 141 includes a controller 141a, which is electrically connected to a head control 142 via a line 143. The head control is connected to the headbox 101 by means of a conduit 144 for sensing a predetermined stock level or pressure within the headbox to maintain the stock level within the headbox at a given predetermined value. The conduit 144 is in fluid communication with a ilow control valve 146 which controls the overow from the headbox 101. A controller 146a associated with the Valve 146 is electrically connected to the header control 142. The electrical output of the header control 142 is connected to the computer control system 120 via a line 147.

The stock passing through the flow meter 148 is then delivered to the stock screen apparatus 10 and therefrom to the headbox 101.

In operation, ilow meters 112, 114, 116, 118, 128 and 148 together with the head control 142 and temperature sensor 138 and diiierential pressure cell 102 provide continuous sampling signals which are applied to the computer control system 120. Therefore, the computer control system continuously produces control signals to operate the various controllers associated with each of the flow control valves within the system.

The preferred embodiment of the screening apparatus 10 incorporated in the control system of the present invention is shown in FIG. 2. The screening apparatus 10 includes a base 11 supporting a main body 12 of substantially cylindrical configuration. An inlet 14 is provided near the upper portion of the body 12 for receiving a supply of fibrous materials suspended in liquid such as paper stock. The material is delivered to a chamber 15 within the housing 12 whereupon the desired constituent of the material passes through a screen member 16 and is collected by an outlet receiving chamber 17. The annular screen member 116, an annular screen member 1.8, a support member 19 disposed between the screen members 16 and 118 and a ring assembly 20I are constructed to form a cylindrical screen assembly 22. The cylindrical screen assembly 22 has the form of -a tube having a hollow space between the inner and outer walls of the tube. That is, the cylindrical screen member 16 is placed concentrically about the cylindrical screen member 18 and spaced radially therefrom by the ring 20.

The support member 19 serves to support the screen members 16 and 18 against the pressure exerted thereon by the incoming material. Material Will fill the chamber 15 and flow over the cylindrical screen assembly 22 to ll a chamber 25 located radially inwardly of the screen assembly 22. Therefore, the desired constituent of material, which is carried over into chamber 25, will pass through the screen 18 and is collected in the receiving chamber 17. The desired constituent of material collected in the receiving chamber 17 is then delivered to a main outlet 27.

The heaviest undesired constituent of the material is separated by a plurality of actions but `chieily by centrifugal force and is collected in a receiving chamber 28 whereupon this undesired constituent of the material is delivered to an outlet 29. Still a further undesired constituent of the material, which is heavier than the desired constituent of material, is separated by gravitational means and falls to the bottom of chamber 15. The bottom of chamber 15 forms a trough 30. An outlet 31 communicates with the trough 30 for receiving the undesired material collected thereby. Another trough 33 is located at the bottom of chamber 25 for collecting the constituent of material unacceptable to the process and which is carried over the top of the screen assembly 22. An outlet 34 communicates with the trough 33 for receiving the undesired constituent of material collected thereby.

One or more rotatable foils 35 extend axially of the screen assembly 22 and radially outwardly thereof and immediately adjacent thereto as indicated by the dotted lines shown in FIG. 2. In the Ipreferred embodiment of the present invention a plurality of foils 35 are spaced equally apart around the periphery of the screen assembly 22. The foils 35 are rotated to clean the surface of the screen member 16 of materials which would otherwise clog the screen. Some of the undesired constituents of the material which are removed from the screen members 16 will fall to the bottom of the chamber 15 into trough 30 and be removed by outlet 31, and some of the undesired material will be carried in suspension over the top of the screen assembly 22 and ultimately collected within the trough 33 and removed by outlet 34.

In a similar fashion a plurality of equally spaced foils 37 extend axially and radially inwardly of the screen 18 and immediately adjacent thereto. The foils 37 are also rotated to remove undesired constituents of the material from the surface of the screen member 18 which would otherwise clog the screen. This undesired constitutent of material is ultimately collected Within the trough 33 and removed via outlet 34.

A better understanding of the detailed construction of the screening apparatus shown in FIGS. l `and 2 can be had by reference to the following description.

The housing 12 consists of an upper portion 40 and a lower portion 41 which are fastened together by a plurality of screws 42 engaging flanges 43 and 44 of the upper and lower portions 40 and 41 respectively. The receiving chamber 17, which communicates with the main outlet 27, is formed by an involute 45 which has the major diameter thereof at an outlet 27, as seen in FIG. 2. An opening 46 is provided in one side of the involute 45 in a plane perpendicular to the axis thereof and concentric therewith. The opening 46 is in direct communication with the space between the screen members 16 and 18 of the screen assembly 22.

A support member 48 is formed concentrically and integrally within the lower portion 41 and extends upwardly within the upper portion 40. Located concentrically within the support member 48 is a sleeve 49. A shaft 50 is journalled by bearings 51, 52, 53 and 54 which are carried Within the sleeve 49. Retainer caps 56 and 57 are secured respectively to the upper and lower ends of the sleeve 49 for retaining the bearings 51, 52, 53 and 54 and the shaft 50 therein. A cover 60 is secured to the upper end of the support member 48, and a seal 61 is carried between the shaft 50 and the cover 60.

A hub 64 is removably connected to the upper end of the shaft 50 and is prevented from rotating relative thereto by a key 65. A contoured nut 66 -threadably engages the shaft 50 to retain the hub 64. One or more arms 68, indicates by dotted lines in FIG. 2, extend outwardly from a ring 69 which is secured to the hub 64. Each of the arms 68 serves to carry one of the foils 35, as seen in FIG. 2. Also connected to the ring 69 are one or more arms 70, and each of the arms 70 serves to carry one of the foils 37. It will be understood that each of the foils 35 or 37 may be ixedly connected to their associated arm or may be removably connected thereto.

The foils 35 have bosses 72 which engage a stifener ring 73 located radially outwardly of the foils. The ring 73 is connected to all of the foils 35 and serves to prevent the foils 35 from flexing axially thereby causing a gap between the foil 35 and the bottom portion of the screen member 16. The foils 37 have bosses 75 which are connected to a stiifener ring 76 radially inwardly of the foils 37. The ring 77 has substantially the same function as the ring 73.

The top portion 40 of the housing 12 is provided with an inlet passage 80 which is formed as an involute as best seen in FIG. 2. The involute 80 has an opening on the inside arcuate portion thereof communicating with the interior of the housing 12 for delivering the material to be screened to the interior of the housing 12.

A cover 82 is secured to the upper portion 40 of the housing 12 by a plurality of studs 83 and nuts 84. A threaded fitting 85 is provided on the cover 82 and may be connected to suitable piping means.

The lower end of the shaft 50 extends into a space within the base 11 and is connected to a multiple V-belt pulley 89. The pulley 89 is rotated by a plurality of belts 90 which are connected to a suitable power source.

Although the specific embodiment of the present invention shows single outlets 29, 31 and 34, it is not to be construed in the limiting sense. The housing 12 may have a plurality of outlets for receiving undesired constituents of material that is delivered to the outlet 29. Furthermore, the housing 12 may have a plurality of outlets around the housing to receive the undesired constituent of material which is received by the outlet 31. Similarly, the housing 12 may have a plurality of outlets in communication with the chamber 25 for receiving the undesired constituents of material therefrom.

According to the present invention the screening apparatus 10 includes a pressure sensing cell 200 positioned within the involute chamber 17 for sensing the stock pressure at the output of the apparatus 10. A pair of pressure sensing cells 2011 and 202 are positioned adjacent the inner and outer screening members respectively. The pressure cells 201 and 202 may be connected in parallel so as to produce an average pressure indicative of the input pressure to the screening apparatus, or may be independent one from the other to monitor the pressure drop across the inner screen as well as the pressure drop across the outer screen.

The accuracy of measuring the pressure drop across the screening apparatus 10 is preferably kept 4within 0.5 inch of water in order to operate the delivery system at the best possible efficiency. Therefore, the pressure sensing devices are preferably air loaded diaphragms 2 inches in diameter positioned either at the inlet and outlet of the screening apparatus or across the screening mechanism therein. The pressure drop across the screening apparatus as sensed by the cells are then delivered to a differential pressure cell, -which is commerically available. By using a zero suppression feature of this type of differential pressure cell, a compensation for the major part of the pressure drop can be made, and a further pressure drop can be recorded or further process the signal which will now only show the top portion of the varying fraction but greatly amplified. This top portion can be expressed in mathematical terms as being a function of variations in fiber quantity, in fiber character and composition and variations in temperature when the flow is constant.

In so recording and displaying this pressure differential and using the primary signal for the further control of the process in a method whereby the main stock valve (stuffgate) supplying the raw furnish to the machine can be controlled through a loop system if the machine is controlled by continuous sampling of various aspects of the system.

In mathematical terms;

Where:

Qzflow of fiber slurry (constant) AW=variation of fiber quantity (consistency) AS=variation of fiber character composition (geometrical shape and surface character as well as fiber type) AT=variation in temperature t=time K1, K2, K3=constants Accordingly, the method and apparatus disclosed herein is based on the premise that the flow of stock to the headbox is constant and that it can be so maintained or if not corrections made to maintain the flow constant since the pressure drop across the screening apparatus for any given ow can be experimentally obtained. Also, the variables that effect the pressure drop across the screen for a given hydraulic and mechanical setup have been experimentally determined. For example, the temperature is keptl constant within one degree range during the process, and the stock characteristics, comprising s'hape of the iiber (slenderness, length, surface, characteristic, etc.) are normally kept within a certain range during the normal paper making process. Additionally, the stock quantity within the slurry (consistency) can be controlled to maintain a predetermined stock characteristic.

The present invention provides a method and apparatus for detecting consistency changes for ber quantity in the range that Was heretofore considered extremely diicult. It will be understood that variations and modifications may be effected without departing from the spiirt and scope of the novel concepts of this invention.

I claim as my invention:

1. A control system for controlling the consistency and quantity of stock delivered to a headbox of a paper making machine comprising:

a plurality of stock supply means for containing stock of different consistencies;

a main stock receiving chamber;

a plurality of ow control means connected between each of said stock supply means and said main receiving chamber for controlling the quantity of each of the ditferent stock consistencies to said main stock chamber;

a flow control device connected in fluid communication with the output of said main stock receiving chamber;

a temperature sensing device for sensing the temperature of stock passing through said flow control device;

a screening apparatus for receiving the stock from said flow control device;

rst and second pressure measuring devices positioned within said screening apparatus upstream and downstream of the stock passing therethrough for measuring the pressure drop across said screening apparatus;

means for adding hot dilutant to said stock between said main stock receiving chamber and said temperature sensing device; and

computer means responsive to said pressure drop and said temperature of the stock to control the flow control means at the output of each of said stock supply means thereby varying the consistency of the stock delivered to said main stock receiving chamber and further controlling said means for adding hot dilutant to said stock to control the temperature of the stock.

2. A screening apparatus for screening fibrous material in liquid suspension to deliver the desired constituent of the material at an outlet of the apparatus to the input of a headbox, said apparatus comprising:

a housing having a plurality of openings defining a a single inlet and a multiplicity of outlets;

a cylindrical screen having respective inner and outer screen members spaced radially apart to form a chamber between;

an involute shaped space within said housing substantially concentric therewith having an opening on one side thereof in a plane perpendicular to its axis for communication with said screen chamber, said involute space having a portion extending outwardly from said housing to form the outlet for passing the desired constituent of material;

rst and second foil means concentrically rotatably carried within said housing adjacent said inner and outer screen members respectively for preventing clogging of said screen members;

drive means for rotatably driving said rst and second foil means within said housing;

iirst and second pressure sensing devices positioned within said housing so as to indicate a pressure drop of stock passing through said housing between said single inlet and the outlet passing the desired constituent of material,

said irst pressure sensing device positioned within the wall surface of said involute;

said second pressure sensing device positioned adjacent said inner screen member for sensing the pressure drop of the stock passing therethrough; and

a third pressure sensing device positioned adjacent said outer screen member for sensing the pressure drop of the stock passing therethrough.

References Cited UNITED STATES PATENTS 1,665,425 4/1928 Van de Carr, Ir. 162-258X 1,975,937 10/ 1934 Graham IS7-92X 2,302,327 11/1942 Kehoe et al. 137-91X 2,626,627 1/1953 Jung et al. 162-259 3,077,924 2/ 1963 Eastwood 162-259 3,196,072 7/ 1965 Wirtz 162-198 3,410,409 11/1968 lRittenhouse et al. 210-137 OTHER REFERENCES Gavelin, Gunnar: Fourdrinier Papermaking, 1963 pages; title page and 15-17.

"REUBEN FR'IEDMAN, Primary Examiner T. A. GRANGER, Assistant Examiner U.S. Cl. X.R. 

